I made a more or less complete compilation of Taeyeon's High Notes from SNSD (and TTS) songs that have been performed live, including lipsynced performances. All the song titles are listed in the video description and pinned comment. Sorry if I missed anything, I tried to gather everything I could think of and remember. Currently Working on a radio performances/song covers/special stages version and also a solo songs version

용서커플 (YongSeo Couple) Named by MCs and fans by using the first letters of their names, meaning “forgiveness” because of the intense disapproval after they were announced to be the newest couple. 고구마부부 (Goguma Couple) Dubbed when SeoHyun was to rate the husband by either saying sweet potato (because of her fondness for sweet potatoes), or hamburger (because she finds them unhealthy). YongSeo Threads in Soompi YongSeo Couple Thread 1 | YongSeo Couple Thread 2 | YongSeo Couple Thread 3​ We Got Married Episodes (English Subbed) Episode 1 - 10 | Episode 11 - 20 | Episode 21 - 30 | Episode 31 - 40 | Episode 41 - 51 RULES I. No bashing of any celebrities/personalities or even any soompi members II. No quoting of pictures III. No one-liners IV. Credit your sources V. No spamming VI. This thread is for Jung YongHwa & Seo JooHyun only VII. Please have fun while spazzing

For me, I think it's Taeyeon solo and I love her first song as solo (I feat. Verbal Jint) is the best song ever~~. Her powerful voice is so so amazing!!!!
This is Taeyeon MV! LET'S check it out!
https://youtu.be/4OrCA1OInoo